This invention relates to a compensating force-measuring or weighing device having at least one working coil movable in an air gap of a fixed magnet system and including means to compensate for temperature incluences in the magnet system. The invention relates, more particularly, to an electromagnetic compensating force-measuring or weighing device of the stated nature.
Decives of this type are known and described, for example, in German Federal Republic Offenlegungsschrift (Laid Open Patent Application) No. 2,400,881. There are usually two available possibilities for compensating the temperature dependence of the magnetic field strength of the permanent magnet system used in such weighing or force-measuring devices. In one case, a temperature-dependent network is connected parallel to its measuring resistor, so that the latter has an opposite temperature coefficient. The temperature-dependent resistor in the network is placed in the best possible thermal contact with the magnet system.
In the second case, low-retentivity materials having high negative temperature coefficients during saturation magnetization are mounted magnetically parallel to the air gap. The material manufactured by the firm of Vacuumschmelze, Hanau, and known by the name of "Thermoflux" (registered trademark) is suitable for this purpose, for example. These materials are usually mounted on the active (magnet) part of the magnet system, and preferably cemented thereto; in rotation-symmetric magnet systems the material is wrapped around the cylindrical active part, for example.
These techniques make it possible to achieve good compensation of temperature dependence with thermal equilibrium in a magnet system. However, if temperature gradients appear in the magnet system which are steeper or even change abruptly at various points, as can occur, for example, when more or less electrical energy is converted into heat in the working coil, the different temperature conditions resulting from point-wise or area-wise application of compensating material and the active magnetic material which extends over a large volume can cause not insignificant problems relating to sufficiently accurate temperature compensation.